1. Field of the Invention
The present invention relates to an underdrain filter block and, more particularly, to a filter block used in draining and backwashing a filtering media in a filter bed and a method of securing the filter block to the filter floor.
2. Description of Related Art
Underdrain filter blocks provide a filter bottom by assembling a number of filter blocks together to provide an upper surface for supporting a filter media. The filter bottom upper surface is provided with openings to allow the flow of filtered liquid from the filter media to pass into the filter bottom where conduits carry the filtered liquid from the filter. The conduits also serve to provide backwashing fluids, such as gas or liquid or both, to the filter media for cleaning. U.S. Pat. No. 5,108,627 to Berkebile et al. discloses a filter underdrain block and is hereby incorporated by reference in its entirety.
Generally, conventional underdrain filter blocks are susceptible to uplift failure due to an internal pressure caused by headloss through the underdrain. The headloss or internal pressure of the conventional underdrain blocks tends to force the block off the filter floor as a bottom section of the underdrain block deflects or deforms from internal pressure.
U.S. Pat. No. 3,956,134 to Sturgill discloses, as shown in FIGS. 5, 6, and 13, an underdrain unit with a bottom wall that extends outwardly beyond sidewalls to define a flange. Perforations in the bottom wall help to secure the underdrain to the floor of the filter basin by engaging with grouting material provided under the underdrain units. Referring to FIG. 6, an end wall of the filter unit is provided with a plurality of perforations that provide mechanical engagement with grouting material provided around the units.
U.S. Pat. No. 6,110,366 to Hunkele et al. discloses an anchor concept for securing an underdrain block to a filter floor. In particular, Hunkele discloses the use of anchors that comprise one or more widenings extending outwardly from a rib so as to form ledges that are embedded in grouting on a filter floor.
U.S. Pat. No. 3,110,667 to Stuppy and U.S. Pat. No. 4,619,765 to Roberts disclose filter block constructions in which a bottom wall of the filter block is defined with ridges or grooves.